Another consideration might be balance requirements. If it looks like its going to come out tail heavy, this would be a good chance to throw in some extra power. I have the O.S. 160 two stroke and the 120 AX. Both really nice motors. I had the 160 in a Giles that weighed around 11 lb. Tons of power. I know you said you didn't need hovering power. I take that to mean the kind of power that lets you pull out of a hover with authority. Even so, I think the 120AX might not be what you're looking for. As stated above, its been tried in this plane and found wanting.
Anyway, just my 2 cents, from a two stroke perspective.